This invention relates to a printing hammer which is for use in a printer head of a printer of the type known as a serial printer in the art and which comprises a piezoelectric actuator or driver operable in a longitudinal mode of extension and contraction.
In the manner which will later be described a little more in detail, such a printing hammer is disclosed in U.S. Pat. No. 4,435,666 issued to Izumu Fukui et al and assigned to the present assignee which was formerly called Nippon Electric Co., Ltd., in English. According to one of various embodiments of the Fukui et al patent, the printing hammer comprises (a) a base member, (b) a piezoelectric actuator having a base end, a free end, and an actuator axis passing through the base and the free ends and having a rest state and an actuated state of extending and contracting along the actuator axis to give a displacement to the free end relative to the base end, (c) an arm having a first line, a second line parallel to the first line, and an end point, (d) a coupler coupling the base end to the base member, (e) a first resilient hinge coupling the free end to the first line, and (f) a second resilient hinge coupling the second line to the base member. The first line serves as a fulcrum of a lever. The second line serves as a power point or point of application. The end point serves as a weight point.
Although not illustrated in the Fukui et al patent in connection with this embodiment, a printing wire or element is fixed to the end point as a load of the lever. In a few other embodiments of the Fukui et al patent, the base end of the piezoelectric actuator is fixed directly to the base member. In any event, the arm is used in transmitting with amplification or enlargement the displacement of the free end of the piezoelectric actuator to the printing wire.
In the above-referenced one embodiment, the first and the second resilient hinges are disposed on both sides of the arm. It has now been confirmed by the present applicants that this arrangement of the hinges relative to the arm results in an energy loss, namely, in an undue consumption of the energy of extension of the piezoelectric actuator.
In a different embodiment of the Fukui et al patent, the first and the second resilient hinges are arranged on only one side of the arm to be parallel when the piezoelectric actuator is in the rest state. It has been confirmed by the instant applicants that this arrangement of the hinges is excellent in avoiding the energy loss. It is, however, inevitable with this embodiment that the printing hammer has a poor amplification factor for the displacement of the free end of the piezoelectric actuator in contrast to the first-described embodiment because of impossibility of disposing the power point adjacent to the fulcrum.
According to several other embodiments of the Fukui et al patent, the displacement of the free end is transmitted to the printing wire with a two-stage amplification by using two levers in series. Due to the two-stage amplification, the displacement amplification factor is excellent despite the fact that the first and the second resilient hinges are disposed on one side of the arm to be parallel when the piezoelectric actuator is in the rest state. It has, however, been confirmed by the instant applicants that the printing hammer is not operable at a high printing speed.